1. Field of the Invention
The present invention relates to a method for transmitting cell Identifier (ID) information in a wireless communication system, and more particularly, to a method for efficiently transmitting additional cell ID information, while minimizing influence on a legacy system.
2. Discussion of the Related Art
A cell ID identifies a cell covering a specific area within a wireless network. The specific area includes at least one Base Transceiver Station (BTS) or Node B that controls wireless operations within its coverage area and provides connectivity between the network and a Mobile Station (MS) or User Equipment (UE) via an air interface. The BTS or Node B or eNode B is an access point for indoor or/and outdoor coverage.
For home coverage, the access point is known as a femtocell Base Station (BS), a Home Node B (HNB), an evolved Home Node B (eHNB), or a Closed Subscriber Group (CSG) BS which is a smaller cellular base station, typically designed for use in residential or small business environments. For the sake of convenience, such a small BS will be referred to as a ‘CSG BS’ or ‘CSG cell’. However, the specific terms are not limited to a certain meaning.
The CSG BS is connected to an operator's network via broadband connection means such as a Digital Subscriber Line (DSL) or a cable. The CSG cell allows cellular operators to extend indoor service coverage, especially where access would be limited or unavailable.
The most challenging issue at this stage of standardization is to define a cell ID for a UE to identify whether a cell is a CSG cell or a non-CSG cell in an early phase of a cell identification process. This is because some UEs are allowed to access the CSG cell, while others are not.
To be more specific, if only higher-layer ID information is used to identify a CSG cell, a UE cannot interpret the higher-layer ID information until it receives the signal through a lower layer and completes initial cell search. If the interpreted higher-layer ID indicates a CSG cell inaccessible to the UE, the UE has consumed unnecessary power and has experienced time latency.
Accordingly, there exists a need for a technique for reducing the power consumption of a UE and minimizing additional delay overhead in a handover process performed for the UE with non-authorized access to a CSG cell.